Glioblastomas (GBMs) are the most common and aggressive tumors of the brain with aberrant resistance to therapies. MicroRNAs (miRs) are small non-coding RNAs that simultaneously suppress and/or activate the expression of multiple protein-encoding genes, and in so doing affect numerous cellular behaviors. Wnt pathway is of fundamental importance to development, tissue self-renewal and repair, cancer occurrence and progression. In GBM, miRs and Wnt signaling are dysregulated and contribute to tumor malignancies and therapeutic resistance. Glioma stem cells (GSC) are a cell subpopulation of primary GBM possess stem cell- like properties and is a key factor in glioma tumor recurrence and therapy resistance. We examined patient-derived GSCs displaying proneural (PN)- and mesenchymal (Mes)-like phenotypes of GBM, and found distinct molecular, biological, and therapeutic response characteristics in each. We also observed that in PN-like GSC relative to Mes-like GSC, two miRs, miR-125b and miR-20b are expressed at substantially high levels and that Wnt signaling is enriched. In vitro and in vivo studies demonstrated that miR-125b and -20b modulate GSC tumor phenotypes. Significantly, there is a positive feedback loop in GSC where Wnt induces miR-125b and -20b while miR-125b/-20b target Wnt inhibitors APC and FZD6, enhancing Wnt activity. Moreover, radiation of GSC induced Mes-like phenotypes, attenuated Wnt pathway and decreased levels of miR-125b and -20b. Based on these novel observations, we hypothesize that miR-125b, -20b and Wnt pathway form a positive feedback loop in GBM, and this interaction regulates malignant behaviors as well as radiation-induced Mes-like GBM phenotypes. To test this hypothesis, we propose to 1) define mechanisms by which miR-125b, miR-20b and Wnt signaling positively influence each other, and in so doing affect GSC malignant phenotypes; 2) determine whether miR-125b and miR-20b regulates GSC malignant phenotypes through Mes- associated genes in a dependent vs. an independent manner and 3) determine whether modulation of miR-125b/-20b and Wnt signaling regulates radiation-induced Mes-associated gene expression and phenotypes, and affects GBM tumor response to therapies. Our studies will help address an existing deficiency in understanding of how aberrant miR expression and Wnt signaling activity contribute to glioma malignancy. This knowledge, in turn, could lead to the identification of novel targets and more effective therapies for treating malignant gliomas.